Method of annealing with a silicone oxidation scale prohibitor



METHOD OF ANNEALIN G WITH A SILICONE OXIDATIQN SCALE PROHIBITOR 3 Claims. (Cl. 148-131) This invention relates to a new process of covering metal surfaces to protect them during heat treating operations.

The process involves the application of silicone compositions to metal surfaces by brushing or dipping prior to subjecting the metal to high temperatures within furnaces.

The purpose of the invention is to lessen and/or inhibit the formation of a thick oxide scale on metal surfaces during heat treating operations by utilizing the silica that forms upon the chemical breakdown of silicone to establish a physical barrier that decreases oxidation.

More particularly, the invention comprises the steps of:

Selecting a silicone compound, Covering the surfaces of the metal with the selected compound,

Placing the metal parts or part in a furnace, Proceeding with a selected heat treatment, Removing the metal partsand Rinsing the surfaces with water removing the silica deposits.

With respect'to the selection of a silicone compound it can be said that all silicone fluid and grease products can be used, for all of them decompose to establish the barrier of silica which lessens the oxide formation on the metal surfaces.

Examples of such silicones are the methyl silicone fluids having the common formulation of where X is an integer of up to 2000 or more.

The manner of use of a selected silicone compound will depend both on its own physical properties and the size of the parts to be heated. For example where a silicone oil is used it is applied by dipping the metalparts into its solution or if the part is of excessive size, a brushing or spraying technique is employed.

Upon removal of a pro-coated metal part from a furnace an inspection will reveal that the silica eflectively United states Patent.

reduced the formation of the oxide scale that otherwise would have formed had the silicone not been employed. In some instances the scale may be negligible and no additional steps to remove the scale need be taken. In other instances a scale is present that requires removal by pickling; however, the time of the pickling operation is substantially reduced. Oftentimes' when silicone is used the scale that forms is removable by pickling where previously the pickling was ineffective, establishing the need for cumbersome molten salt baths to remove the dense,-thick, oxide scale. These beneficial results occur because the silicone coating readily burns almost immediately upon its introduction to the high temperatures within the furnace, giving off a dense fume that has the tendency to remove oxygen from the spaces adjacent to the metal surfaces. Also the fume deposits finely divided silica particles on the exposed metal surfaces, thereby forming a protective coating that bars the oxygen that remains and/or returns to the spaces adjacent to the metal surfaces.

To point out how time is saved by using silicone, the following comparisons are made in conjunction with the heat treating and pickling operations of 17-7 PH stainless steels: I

Three heating periods are required, one at 1800 F., one at 1400 F. and another at 1100 F. The time required during these periods remains the same whether silicone is used or not. However, the presence of silicone during the heating periods reduces the between period intervals very substantially. Formerly after the 1800 F. heating period, apickling bath required approximately twice the time now needed to remove the scale before the metal is reheated'to 1400 F.

With respect to the heating period at 1400 F., the subsequent pickling operation was very extensive and then after the 1100 F. heating period further pickling was necessary. Now with the use of silicone the only break that occurs between the 1400 F. and 1100 F. heating periods is for necessary cooling and at the conclusion of the 1100 heating period, a pickling bath is employed for only a limited time. ,A sheet of the 17-7 PH stainless steel approximately a foot square, formerly required eighty-five minutes total for the time expended in the two pickling baths after the 1400 F. and 1100 Ff I heating periods, whereas with the pre-application of a silicone coating only five minutes of pickling tirneare requiredfto remove the undesirable oxide scale. I

This favorable reduction in the pickling time that is. consumed in removing the surface oxides is not singularly associated with 17-7 PH stainless steels but it is generally characteristic whenever metals are pre-coated with silicone.

Although a substantially uniform direct coating of a silicone on a metal surface is known to be the best way possible to derive the benefits of this process, it has been determined that direct application of the silicone is not absolutely necessary Where less favorable results will be acceptable. The presence of a'source of silicone within a furnace will oftentimes result in the emanating fumes depositing sufficient quantities of silica on the exposed metal surfaces to reduce theformation of oxide. Where this proves satisfactory a separate furnace attachment is used to admit silicone fluids to the furnace interior. I

Also, where small parts are placed in a large furnace, at smaller encompassing container with restrictive vents is placed around the parts to confine the dispersion of the silicone fumes thereby preventing the escape of silica.

I claim:

1. The process of annealing metallic articles comprising the application to the surfaces to be annealed a silicone fluid, and the subsequent heating of the articles to a temperature sufiiciently high to decompose the sili cone'fluid at the outset of the annealing covering the surfaces with finely divided silica that settles out from the dense fumes thereby preventing oxidation of the surfaces during anneal'mg.

2. The process of heat treating metals comprising the application of silicone compounds to the metal surfaces and the heating. of the metals at an initial temperature sufiiciently high to decompose the silicone compound at the outset'of the heat treating thereby preventing excessive oxidation of the metal surfaces by means of the surface deposit of finely divided silica resulting from the zfidimating the metals at an initial temperature sufii- -iiefiemmesfiied in ilh file of thi pat nt UNITED STATES PATENTS 1,085,168 Thompson Feb. 3, 1914 Webb et al. May 17, 1949 Jennings etal "June 21, 1949 Zurcher Jan. 24, 1950 Claws'on Feb. 21, 1950 Pipkin Mar. 20, 1951 

1. THE PROCESS OF ANNEALING METALLIC ARTICLES COMPRISING THE APPLICATION TO THE SURFACES TO BE ANNEALED A SILICONE FLUID, AND THE SUBSEQUENT HEATING OF THE ARTICLES TO A TEMPERATURE SUFFICIENTLY HIGH TO DECOMPOSE THE SILICONE FLUID AT THE OUTSET OF THE ANNEALING COVERING THE SURFACES WITH FINELY DIVIDED SILICA THAT SETTLES OUT FROM THE DENSE FUMES THEREBY PREVENTING OXIDATION OF THE SURFACES DURING ANNEALING. 